This application relates to nucleotide regulatory sequences and their binding factors.
Plants have evolved a diverse array of mechanisms for protection against a variety of pathogenic organisms. Pathogen-derived signals such as elicitins, harpins, fungal cell wall fragments, avirulence (avr) gene products, and metabolites specified by avr gene products are recognized by receptors that trigger a conserved set of defense responses. Perception of these signals induces changes in protein phosphorylation that are thought to affect a variety of defense responses. Such defense responses include lignification of cell walls, induction of pathogenesis-related (PR) genes such as those encoding chitinases and glucanases, production of antimicrobial phytoalexins, induction of systemic acquired resistance, and generation of reactive oxygen species involved in crosslinking of cell wall proteins and induction of programmed cell death. These responses are instrumental in suppressing the growth and spread of a pathogen within the plant host.
Many of these defense responses are dependent on the transcriptional induction of specific genes in response to appropriate signals. For example, when solanaceous plants such as tobacco and potato are challenged by a pathogen or elicited by various pathogen factors, a major metabolic shift occurs where sterol production is suppressed and sesquiterpene phytoalexin synthesis is induced. The first step specific to sesquiterpene phytoalexin biosynthesis is a cyclization of the isoprenoid intermediate FPP by enzymes generically referred to as sesquiterpene cyclases. In tobacco, the sesquiterpene cyclase 5-epi-aristolochene synthase (EAS) produces 5-epi-aristolochene, followed by the addition of two hydroxyl groups to yield capsidiol. The sterol-specific branch of the isoprenoid biosynthetic pathway also extends from the intermediate FPP. Declines in sterol biosynthesis have been correlated with suppression of squalene synthase enzyme activity, and the induction of sesquiterpene biosynthesis with an induction of a sesquiterpene cyclase enzyme activity. Because these two enzymes are positioned at a putative branch point in the pathway, the induction of one enzyme and the suppression of the other were interpreted as an important mechanism controlling carbon flow and, hence, end product formation.